One method of taking samples of fluid from a patient, such as blood samples, is to utilize a double ended needle in which one end is used to accomplish a veni-puncture and the other end is adapted to be connected to one or more partially or fully evacuated tubes which may or may not contain medicament. The samples are collected due to the pressure differential produced when the interconnection is made. Naturally when collecting samples of fluid such as blood it is desirable to provide a complete fluid path during the collection process but also to avoid any danger of changes in pressure producing backflow of contaminated blood or other fluid, such as medicament, to the patient. Medicaments are contained in the tube for mixtue with the blood and together or independently could flow back through the needle assembly into the patient. Thus, it has been found that various types of check valves can be employed as part of the needle assembly to achieve the necessary protective measures to avoid backflow.
When samples are collected on mass scales, cost is a factor particularly where disposability is desirable and in modern day technology is often of the essence. Therefore, the more complex the needle assembly, the most expensive it becomes and, thus the more undesirable it becomes for disposability purposes. Accordingly, in many instances it is been found to be a more or less prohibitive additional cost to provide complex valving mechanism including a check valve to avoid backflow as part of a disposable low cost needle assembly for collecting single or multiple blood samples.
Therefore, it is of extreme concern that the problem of backflow be avoided while maintaining the needle assembly at the lowest possible cost. Consequently, there is room for improvement in the combination structure utilized for sampling purposes.